The present invention pertains to improvements in the field of pyrolysis. More particularly, the invention relates to an improved horizontal moving bed reactor for pyrolyzing particulate material.
Pyrolysis has become an attractive solution to the growing environmental problems caused by the generational and worldwide accumulation of scrap tires and automobile shredder residues. Applicant has already proposed in U.S. Pat. No. 4,740,270 to treat scrap tires by vacuum pyrolysis. Used rubber tires in the form of cuttings are decomposed under vacuum at about 360.degree.-415.degree. C. to useful products such as carbon black, hydrocarbon oils and gas. In U.S. Pat. No. 5,451,297, Applicant has proposed to also treat automobile shredder residue by vacuum pyrolysis with a view to recovering commercially valuable products. In either case, the pyrolysis is carried out in a multi-tray reactor having a plurality of spaced-apart heated trays arranged above one another and each receiving a bed of cuttings or shreds charged onto the uppermost tray of the reactor. The bed of particulate material is transported from an upper to a lower tray by means of scraping arms which slowly move the particulate material on each tray towards and into a discharge orifice in the tray so as to fall on a lower tray. The trays are heated at temperatures to provide a vertical temperature gradient between the uppermost and lowermost trays with the lowermost tray being heated at a temperature higher than the uppermost tray.
Applicant has observed that the layer of material in contact with each heated tray inhibits efficient heat transfer from the heated tray to the center of the bed. Where the particulate material subjected to pyrolysis is a carbon-based material such as rubber tire, the particles of rubber in contact with the heated tray become coated with a layer of carbonaceous material and such a carbon layer acts as a heat insulator to further inhibit heat transfer. The same problems occur when the material is exposed to overhead heat radiation.